I've done a bit of home work on the Easy As RDF requirements and would like to double check the suitability of the yagi's beamwidth when used for RDF. The current design ends up being a manageable 523mm boom length, 3 directors and a 328mm dipole tip-to-tip. This gives a 65 deg beamwidth, which seems OK for the purpose. Any thoughts on this? What would you say is a good beamwidth for actual site conditions, assuming for the moment that any boom length is OK?

Also, I'm somewhat unclear on the merits of single versus folded dipoles

Basically what we have here is a piece of 30mm PVC pipe with T fitting and a second piece of pipe that acts as a handle for the completed item. (btw, check that you can get saddle clamps for 30mm PVC, 25mm PVC may be easier)

The black sguigly line is the RG-59 cable. It has an SMA connector on one end (to attach to the receiver), goes into a balun circuit before being attached to the dipole. (The phrase balun circuit strikes fear into the hearts of many people, but it is just a loop in the cable with the sheath copper being connected on all three parts, the centre copper being connected at two ends and then, along with the third end, being connected to the dipole) Click the balun button in the yagi calculator to get a better picture.

The reflector is a strip of flat aluminium, 10X3 mm and 335 mm long attached to the PVC pipe with a plastic saddle clamp and pop rivets.

The dipole is a piece of flat aluminium 10X3mm and 685 mm long folded twice around a 35mm plug to form a flat sided oval/rectangular loop 331mm tip to tip with a gap in between the ends of 10mm, then attached to the PVC pipe with a sadle clamp and pop rivets securing the two ends. Attach the copper ends from the balun with the pop rivets at the same time.

The Directors are just strips of 10X3mm aluminium attached to the PVC pipe using saddle clamps and pop rivets.

Things to watch:

Make sure that the aluminium strips are cut to the right lengths within 2 mm. Spread the various pieces along the PVC pipe within 2 mm of required spacing.Make sure the balun loop is within 2mm. When you look at the assembled unit from behind, all the directors, dipole and reflector are in the same plane.Make sure the directors, dipole and reflector are mounted at right angles to the PVC Pipe.

That said, don't stress too much about it, even if you are just close, you will find the antenna is much more powerful and a lot more directional than a standard rubber duck antenna.

Adding more directors to the antenna will decrease the beamwidth and increase the gain, but also make the antenna much longer so you need to accept a tradeoff at some point. Personally, any beamwidth less than 90 degrees makes it fairly easy to find things and I have a 3 element Yagi which works just fine.

A Yagi is just one type of Directional Antenna. As Paul mentioned, quads work very well, metal down pipe is quite effective and a pringles tin can do unbelievable things in the 2.4gHz range. Its really a case of what your preference is. Quads are very easy if you can etch PCB's, if you can't, a Yagi is an excellent alternative.

Here's one for all the rocket scientists among you, if you would pardon the unintended pun:

Its all fun and games to design and make your yagi antenna to work with the RDF tracker, but how do you test the impedance (which needs to be 50 ohm) if you have no vector network analyzer and generally also no clue!?! Certainly it can't be as simple as just using a 50 ohm cable, such as RG-58c?!?

Here's one for all the rocket scientists among you, if you would pardon the unintended pun:

Don't knock it, I've even got the T-shirt!

how do you test the impedance (which needs to be 50 ohm) if you have no vector network analyzer and generally also no clue!?! Certainly it can't be as simple as just using a 50 ohm cable, such as RG-58c?!?

Why using your network analyser of course!

Don't worry too much. Build it as per the spec (including the balun or match) and try it out. Small impedance mismatches are MUCH less important when you're only receiving.If you want to find out more, google something like SWR antenna

I have just completed reading this wonderful thread. From your comments, and detailed calculations of your array elements, it appears clear that you have a strong grasp of the science and engineering of antenna geometry.

I have just ordered two of these EasyRDF units was interested in your comments.

Last weekend, I was over at Georges Shed and had the opportunity of having a good look at your RDF configuration especially your yagi antenna for the 433 Mhz “Wooshtronics” EasyAs RDF beacon, that you had assembled.

What have your field result been like.

WOW!What a nice looking piece of kit.

I must admit to being highly impressed with the simple and easily replicatible construction method, that you used for of this antenna."Genius can be best described as being the art of simplicity"

Your use of PVC conduit, aluminum stripping, conduit saddles and a few pop rivets, was indeed inspiring.

However there are few issues, I was not sure of and had hoped that you could assist me further some details of the calculations used in your design.

When I arrived George was however trying to obtain some directionality with your scanner and the flat element antenna. Being at a relatively close distance to the transmitter was almost impossible to George to be able to turn a direction of the actual unit. So I suggested that we decided to take a walk down the hill; over and road; through the creek and round the corner. Unfortunately even at this distance (about 150 m) from the beacon, the signal was still being strongly flooded across all directions, that the antenna was pointed. The result being that we were still unable to easily determine the direction from the rocket.

NARROW BEAM VS BROAD BEAM

Now, we all know that at a distance of 150m in a flat open at paddock that you could probably see the rocket and would not be using the RDF gear anyway Now I know, the flat level open ground 150 m is nothing however in a square grid of size (22500sq/m) in a cornfield, then such a task may almost become exhausting.

RADIOSHACK PRO 93

As it happened . I had also brought with me to George’s my own Radio Shack Pro 93 Dual Trunking 300 Channel Scanner($20-00 EBay a few years ago) and a timber and 4mm brass rod five element Yagi Antenna, that I had constructed and used some time ago for other 433Mhz RF beacon sources.

(I regret only be able to a small fraction of features of this unit and would welcome a fast tutorial from anyone professing a solid understanding of Dual Trunking Scanners.)

We therefore decided to see if changing to this unit would give us any better a result with a the “Wooshtronics”beacon. Immediately when we turned the brass rod yagi towards the transmitter the receiver responded with loud clear tone, that remained constantly at about 20 Degrees of Beam regardless of the distance from the beacon.

Now all of these test do "live or die" in the field. We have as yet not tested either antenna a range of 1000 meter plus, in heavy woodland or through cultivation. I noted in your spec you listed your gain as being 3 db ? Surely you are mistaken or am I not understood your spec. I had always thought that most Yagi's were high gain antennas (10-16 db) with the higher the better. I have always operated on this assumption and I have no clear recall (this happens when you get older!), of where I picked up that concept.

It was then that I casually observed that while both antennas were five element Yagi (4 x Drivers 1 x Active Element and 1 x Reflector ) constructed to 433 Mhz, that they varied greatly in their overall geometry. As it had been some four years since my antenna had been constructed, I felt I should check my original calculations to ensure that I had adhered To my own calculations during the construction.

I have listed these details are below, along with a copy of my original calculations.

My 433Mhz 5 Element Yagi Antenna dimensions spacing and layout.(Please note the differential between the spacing of my Reflector and the Active Element and yours)

I will readily admit to only having a rudimentary knowledge of antenna geometry and RF radiation patterns I fear I may certainly need to solicit the opinion and intellect of persons/beings, vastly superior to mine. I am afraid that my ONLY basis of knowledge was the little that I managed to glimmer in the 1970s, when I served as a radio officer in a CMF artillery regiment.

(OK let me just say that for ALL those of you who are now thinking. “Wasn't that NOT long after radio was first invented ” - all I can is - "That is COLD!")

I guess my rudimentary knowledge of antenna geometry is confined to derivatives of “quarter wavelength squared” type calculations. I therefore have been forced require all the published drawings, software like Quickyagi and on-line calculators, that have been cleverly devised and calculated by others. In other words I mean NO offense is questioning you antenna layout. Perhaps the width of the elements (being 12mm Flat Aluminum has a profound effect on the radiation pattern)

I am therefore at pains to be able to explain why there should be such a big differences in element spacing and length of an antenna that is constructive similar frequency range to mine. I also wonder the broad beam of your antenna could be effected by affected by the use of flat 12mm wide aluminum strips for elements in your waveguide of your antenna as compared to the 4 mm brass rod used in mine.

Thanks for the kind comments, but please be under no illusion as to how much I know about antenna's! I received a lot of help from PK, Buzzard and Yagi design software. The software tool makes it easy to design a workable yagi with virtually any set of materials, gives you detailed construction info and then you need to just assemble it.

As far as the easy-as RDF's close range directionality is concerned, a critical bit that needs to be understood is that at close range the signal strength is so high that it basically gives good signal strength in any direction. Though this definately becomes more predictable at greater distances, the solution is to simply squelch the signal or, at really close distances, de-tune the receiver by say 0.005 MHz. The receiver will then be much more decerning where you point the yagi. This is actually very well explained in the packaging that the Easy-as RDF came in from Whooshtronics.

I must say that I would have thought you would have had more success at 150m, but again the squelch is the critical bit. I've used that rig on 2 occasions, once as a test in my street starting at a range of about 600m and then again at a recent launch of Helldriver, working from a range of maybe 250m. Both times the squelch was really enough, because by the time you got within 30m or so, you could hear the beeper. I reckon the system works very well

I'm heading over to George's this weekend and I'd be happy to demonstrate. As far as specific tech-help is concerned, I would suggest you talk to the blokes at Whooshtronics as they know this stuff cold.

We had our public launch today, lots of fun and many rockets. I had the opportunity to give the Easy-As RDF a real test. Helldriver went up with an I285R to about 4000 feet (haven't checked the flight data yet) and drifted a long way due to a bit of wind. It touched down what I would guess to be about a kilometer away in an area that was partially obscured from view due to a slight rise in topography. I didn't know which side of the nearby road it had gone down on or whether it was in the open paddock or the adjacent corn field. In addition I had a visual bearing on it, but couldn't follow it directly as it crossed several fences.

Fired up the receiver and immediately got signal. George and myself walked up the track and then up the road. The, at first, audio only signal slowly increased to a 5/10 signal on the bar graph and with a bit of squelching the signal was ultra directional. We went as far as the road could take us, jumped the fence and basically walked straight to the rocket.

I reckon the Easy-As RDF saved me a lot of time and uncertainty. I probably would have found the rocket eventually because it was in the open paddock, but if it had been in the corn field it would have been gone for sure. The EARDF is well worth the investment.

Tarpazium posted some pictures that are really similar to the design I have found to work the best for VHF and UHF stuff, I just wanted to add my two cents in case it's something that anybody will find useful. Impedance matching here is a big concern and most of the time with a Yagi Uda, that is done using a gamma match at the feed point of the driven element. The benefit there is that you don't have to isolate your elements from the boom. It can all be welded together if you have the equipment and want to make one out of aluminum. More durable, but also more expensive to make in most cases.

The half-wave folded dipole driven element is going to start out with a feedpoint impedance of somewhere around 300 ohms and needs a gamma match. However, the driven element in the image posted by Tarpazium is something a little different, it's more like 3/4ths of a half wave folded dipole. This one will have a feed point impedance of only about 150 ohms by itself. By the way, it doesn't matter which side of the driven element you connect the coaxial feed line shield and core to, the whole thing is going to radiate anyway. To bring the impedance down closer to 50 ohms with this type of driven element, you actually use your parasitic (Reflector and directors) elements to adjust the impedance. This is something that was devised by Kent Britian WA5VJB and subequently placed first and second in a contest. The guy who got first place copied Kent's design and the guy who was in second place was Kent. I'll link a PDF below created by Kent that explains the construction of this antenna in detail and even covers the additional steps if you want to construct a dual band version for 2 meter and 70 centimeter. I hope somebody finds this information useful. I have worked low earth orbit satellites with this design using a five watt handheld radio so it ought to work just fine for something still in earth's atmosphere.